getMenuPresenters

Create main menu/popup menuitems. Null values will be later replaced by JSeparators.
This method is called for popups and for menus. It's called each time a popup menu is contructed and just
once for the main menu. Main menu updates happen through the synchMenuPresenters() method.
If you want different behaviour for menu and popup,
use a different implementation returned by Presenter.Popup and Presenter.Menu.